1. Field of the Invention
The present invention relates to a color video signal demodulating apparatus for demodulating a color video signal in which an abnormal color burst having a phase different from that of a regular color burst is inserted in a predetermined horizontal scanning period, as in a color video signal in which a macro vision signal is recorded for copy guard, for use in DVDs or the like.
2. Discussion of the Related Art
In the DVD or the like, a macro vision signal is recorded for copy guard. The signal is a pseudo horizontal synchronizing signal added to 1 H of the Vertical Blanking Interval (VBI).
In some cases, the color burst is subjected to phase inversion. For example, although a color burst of eight waves of 3.58 MHZ is usually inserted in a back porch, an abnormal color burst is inserted such that 5.5 waves of the former half have the same phase and 5.5 waves of the latter half have an opposite phase. Such a color burst exists in a predetermined horizontal scanning section (H). For example, color bursts of 2 H repeated every 17 H or 4 H repeated every 22 H are such inversion bursts. This inverted color burst is described in U.S. Pat. No. 4,577,216. (However, the inversion burst position and 5.5 waves are not mentioned therein.)
If such a video signal is to be recorded or reproduced by a video tape recorder (VTR), the pseudo horizontal synchronous signal causes an automatic gain control (AGC) circuit to malfunction when the AGC is performed at the VTR recording portion. Furthermore, the inversion color burst causes a color signal crosstalk improvement circuit to malfunction, which is provided at the VTR color signal recording/reproducing portion for suppressing color signal crosstalk between neighboring tracks (color signal crosstalk between fields). With these circuits in the VTR being malfunctioned, the reproduced image quality deteriorates to a level not acceptable to practical use, thereby achieving the function of "copy protection." As a result, normal recording becomes impossible.
In particular, in reproduction of a video picture recorded by the inversion burst, stripes of certain color are displayed on a screen. However, when such a video signal is demodulated by an ordinary NTSC color TV receiver, the signal is properly demodulated and displayed.
The video signal thus provided with the macro vision signal for copy guard of the DVD or the like causes no deterioration of the picture quality when it is demodulated by the NTSC color TV receiver. Therefore, no particular measure has been taken on the receiver side for modulating the macro vision signal.
In the case of the inversion burst, although the picture quality is deteriorated due to differences in hue and color saturation between the inversion burst line and the normal burst line, in general, such deterioration of the picture quality can hardly be noticed by viewers. Thus, no subjective deterioration of the picture quality occurs.
However, when the picture source is changed, for example, the DVD and TV broadcasting are interchanged, the viewers can see a difference between the displayed pictures, i.e., the deterioration of the picture quality is readily recognized under objective evaluation.